In image forming apparatus, such as electrophotographic copiers, printers and the like, the surface of a latent image carrying member, such as a photosensitive drum or the like, is charged by a charger. An electrostatic latent image is formed on the charged region by an image exposure, and the latent image is developed so as to be rendered visible. The developed image is transferred onto a transfer member, and fixed on the transfer member.
Various types of chargers are commonly known, and these can be broadly divided into corona chargers and contact chargers. Corona chargers use a corona discharge to form the electrostatic latent image on the surface of an electrostatic latent image carrying member, whereas contact chargers include a charging brush, charging roller or rotatably driven endless charging belt which is brought into contact with the surface of an electrostatic latent image carrying member.
Chargers using a corona discharge are advantageous in that they provide stable charging, but are disadvantageous insofar as they generate large amounts of ozone which cause deterioration of the latent image carrying member and is harmful to humans. Contact chargers, however, generate markedly less ozone than corona chargers.
Among contact chargers, those using drive type rollers and belt have complex constructions due to the necessity of a means to implement the drive. Stationary type contact chargers which use a blade or film as a contact member for charging are advantageous inasmuch as they are inexpensive and compact.
An example of such a blade type contact charger is shown in FIG. 16. This type of charger is provided with a blade B as a contact member which makes contact at a predetermined position with the surface of a charge-receiving member N, such as a photosensitive member or the like, in at constant region L, and which charges an interval between the surface being charged and a region M separated from the surface being charged and contiguous with the region L.
In stationary type contact chargers wherein a contact member used for charging is arranged at a predetermined position relative to the charge-receiving member having a moving surface, or wherein the contact member charges the surface of a charge-receiving member by making contact with the surface of the charge-receiving member which moves relative to the contact member, dirt readily accumulates in the aforesaid charging region M of the contact member with repeated use of the contact charger, thereby causing irregular charging, and ultimately causing image irregularities due to the irregular charging.
Thus, a need exists for a contact charger which eliminates the previously described disadvantages of conventional contact chargers.